The present invention is related to medical devices, systems, and methods, and is also relevant to robotic devices, systems, and methods for their use in medical and other robotic applications. In one embodiment, the invention provides a grip actuation system within a master/slave robot arrangement to give a system operator tactile feedback of grip strength when gripping small objects.
Minimally invasive surgical techniques are intended to reduce the amount of an extraneous tissue which is damaged during diagnostic or surgical procedures. By reducing the trauma to surrounding tissues, patient recovery time, discomfort, and deleterious side effects can be reduced. While many surgeries are performed each year in the United States, and although many of these surgeries could potentially be performed in a minimally invasive manner, only a relatively small percentage of surgeries currently use the new minimally invasive techniques now being developed. This may be in part due to limitations in minimally invasive surgical instruments and techniques, as well as the additional surgical training involved in mastering these techniques.
While known minimally invasive surgical techniques hold great promise, there are significant disadvantages which have, to date, limited the applications for these promising techniques. For example, the standard laparoscopic instruments used in many minimally invasive procedures do not provide the surgeon the flexibility of tool placement found in open surgery. Additionally, manipulation of delicate and sensitive tissues can be difficult while manipulating these long-handled tools from outside the body. Many surgical procedures are complicated by the limited access provided to the surgical site, in which tools and viewing scopes are often inserted through narrow cannulae, all while viewing the procedure in a monitor which is often positioned at a significantly different angle than the patient.
To overcome these disadvantages, minimally invasive telesurgical systems are now being developed. These systems will increase a surgeon""s dexterity and effectiveness within constrained internal surgical sites. In a robotic surgery system, an image of the surgical site can be displayed adjacent master input devices. The system operator will manually manipulate these input devices, thereby controlling the motion of robotic surgical instruments. A servomechanism will generally move surgical end effectors in response to the operator""s manipulation of the input devices, ideally providing translation, rotation, and grip actuation modes. As the servomechanism moves the surgical end effectors in response to movement of the input devices, the system operator retains control over the surgical procedure. The servomechanism may move the devices in position and orientation, and a processor of the servomechanism can transform the inputs from the system operator so that the end effector movements, as displayed to the system operator at the master control station, follow the position and orientation of the input devices as perceived by the system operator. This provides the system operator with a sense of xe2x80x9ctelepresencexe2x80x9d at the internal surgical site.
The robotic surgical systems now being developed show tremendous promise for increasing the number and types of surgeries which may be performed in a minimally invasive manner. Nonetheless, these known systems could benefit from still further improvements. For example, although force feedback systems for robotic surgery have been proposed, the added cost and complexity of these proposed force feedback systems has often limited their implementation. Additionally, work in connection with the present invention has shown that known force reflecting master/slave robotic arrangements without force sensors may not be ideal for implementation of tactile feedback to the system operator in all the actuation modes within a telesurgical system, particularly in grip.
In light of the above, it would be desirable to provide improved surgical devices, systems, and methods. It would also be desirable to provide improved robotic devices, systems, and methods, both for use in robotic surgical systems and other robotic applications. It would be beneficial if these improvements enhanced the operator""s control over, and tactile feedback from, the robotic end effectors. It would further be desirable if these improvements did not unnecessarily complicate the system, and if these improved techniques recognized differences between grip and other actuation modes that might justify specialized grip systems.
The present invention provides improved robotic devices, systems, and methods, particularly for use in telesurgical systems. In general, the invention provides an improved master/slave arrangement for enhanced telepresence, particularly for grip actuation within a multiple degree of freedom telepresence system. By applying the present invention, slave grip strength can be enhanced and/or tailored when master grip elements approach their closed configuration, rather than relying on gripping forces which are only a function of position error.
The invention provides an enhanced sense of feel by using a programmable grip strength amplification, generally without having to resort to slave force sensors. Instead, a grip error signal can be artificially altered beginning at a predetermined grip configuration. For example, where a grip input handle includes first and second grip members that move relative to each other to define a variable grip separation, and where an end effector similarly includes first and second elements defining a variable end effector separation, when above a predetermined grip separation, actuation of the grip members will preferably result in one-to-one corresponding actuation of end effector elements. This allows, for example, a robotic surgical system operator to change the separation angle of the jaws of a surgical forceps by corresponding changes to a separation angle of an input handle. In many embodiments, contact between the elements of the forceps may begin just as the gripping members pass the predetermined grip member separation (assuming the jaws are free to move with negligible tissue or other matter between the jaw elements). Continuing to squeeze the grip members beyond this predetermined point can quickly impose the maximum allowable gripping force on the jaws, thereby allowing the jaws to squeeze very small or thin objects such as sutures, tissue membranes, and the like, without having to push the grip members to an unnatural angle. In the exemplary embodiment, a biasing spring assembly may be provided between the grip members, with the grip members beginning to compress the spring assembly just as they pass the predetermined grip enhancement point. This provides tactile feedback to the robotic system operator indicating that the enhanced grip strength is being applied, and can simulate the resilient deflection of handles (such as the handles of a medical forceps or hemostat) felt when squeezing a small object using a traditional surgical tool.
In a first aspect, the invention provides a method comprising squeezing first and second grip members together with a hand of an operator. First and second end effector elements are moved in response to the squeezing of the grip members according to a control relationship. The control relationship is altered when the grip members are near a closed configuration.
The end effectors will often be moved by applying following forces in response to a misalignment between a grip separation (between grip members) and an end effector separation (between end effector elements). The separations may comprise angles, linear distances, vectors, or the like. In an exemplary embodiment, the moving step can be effected by measuring separations between the grip members and between the instrument elements. The end effector elements can then be moved by producing an error signal from a comparison between the measured grip separation and the measured instrument separation. The error signal will typically be enhanced when the grip members are adjacent a closed configuration. More specifically, the error signal may be enhanced by artificially altering the measured grip separation, preferably according to a continuous invertible function. By selecting a function which only alters the measured grip separation below a predetermined value, the end effector elements can follow the grip members with a one-to-one correspondence when the grip members are relatively wide open. In this relatively wide configuration, while it is generally desirable to have one-to-one following when no forces are applied against the end effectors, it may be acceptable to have significant angular misalignment (for example) between the grip members and the end effector elements when imposing high gripping forces. However, by increasing the sensitivity of the system to misalignment (and hence the grip strength) once the grip members come closer together, the instrument elements can apply the maximum gripping forces against a very small gripped object (such as a suture) without requiring the system operator to push the gripping elements together to an unnatural xe2x80x9coverdosedxe2x80x9d configuration.
Tactile feedback to the system operator of the altered gripping forces may be provided by driving the gripping members in response to the member/element misalignment using a reciprocal master/slave arrangement, and by altering the master error signal when the slave is nearer the closed position, ideally so as to provide a servo-mechanism with overall stiffness matching that of a desired tool. Alternatively, a simple feed forward system can provide tactile feedback to the operator by including a biasing mechanism in the gripping structure. This biasing mechanism can impose different reactive forces against the operator""s hand beginning at the predetermined force enhancement point or biasing transition point.
In another aspect, the invention provides a robotic system comprising a master controller having a biasing system and first and second grip members defining a grip separation. The biasing system urges the grip members apart (typically with a varying force) so as to define a predetermined grip separation. A slave has first and second end effector elements, and defines an end effector separation therebetween. A servomechanism couples the end effector elements to the grip elements and applies a following force to the end effector elements. The servomechanism applies a first following force when the grip is wider than the predetermined separation, and a second following force when narrower than the predetermined grip separation. The biasing system thereby provides tactile feedback to the operator of a change in grip strength. In some embodiments, the biasing system comprises a variable rate spring which provides a varied tactile feedback at a biasing transition point.
The master controller will often be moveable with a plurality of positional and/or orientational degrees of freedom. The servomechanism may move the slave in a corresponding plurality of degrees of freedom in response to the positional and/or orientational movement of the master. In many embodiments, the positional and orientational force rates imposed by the servomechanism may remain substantially uniform throughout positional and orientational ranges of motion, the forces typically being based on the master/slave misalignment, or positional and orientational difference between the master and slave. In other words, the enhanced grip of the present invention may be specifically applied to actuation in the gripping mode.
The separation between the grip members and/or end effector elements will often comprise angular openings, although they may alternatively comprise linear separations between parallelogram linkages, or the like. These enhanced grip force techniques are particularly useful for actuating the jaws of surgical instruments such as forceps, scissors, clip appliers, clamps, or the like. Advantageously, the system may be capable of applying enhanced following forces which are tailored to the strengths and/or intended uses of these differing surgical tools, allowing these differing end effectors to be detached and sequentially secured to the servomechanism without having to alter the master controller.
In yet another aspect, the invention provides a robotic system comprising a master controller producing a master position signal in response to a position of the master along a first degree of freedom. A slave end effector produces a slave position signal in response to a position of the end effector along a first degree of freedom. The slave has a constraint limiting movement in the first slave degree of freedom. The end effector moves in response to an error signal. The error signal is defined at least in part by a difference between the master position signal and the slave position signal. A processor couples the master to the slave. The processor enhances the error signal when the slave is adjacent the constraint.
In another aspect, the invention provides a surgical robotic system comprising a master controller having first and second grip members defining a grip separation. An end effector having first and second end effectors is coupled to an actuator such that actuation of the end effector decreases the end effector separation. A processor is operatively coupled to the master controller and to the actuator such that when the amount of end effector separation is above a certain separation value, a decrease in the grip separation of the master controller controls the amount of end effector separation. When the end effector separation reaches a certain separation value, a further decrease in the grip separation controls the amount of force applied by the end effector.
In yet another aspect, the present invention provides a surgical robotic system comprising a master controller having first and second grip members that define a grip separation. An end effector having first and second end effectors and an end effector separation between the first and second end effectors is coupled to an actuator such that actuation of the end effector decreases the end effector separation. A processor is operatively coupled to the master controller and to the actuator such that when the end effector separation is above a certain separation value, a decrease of the grip separation of the master controller controls the amount of end effector separation. Upon the grip separation reaching a certain separation value, a further decrease of the grip separation controls the amount of force applied by the end effector.